Great thread. I wanted to open similar one, but no need for that i will comment here.
Demography and demographic statistics are my hobby so i have knowledge about many states and most major cities on this topic.
To OP´s ranking based on continents and foreign born population above 5,000. Not accurate measurement, not saying totally wrong one, no, but 1st of all it should go to % share of total population and at least count in also 2nd generation immigrants.
To diversity or multiculturalism or how to call it - there is diversity also between 2 neighbouring countries - ethnicities and regions inside those countries, but obviously there is greater diversity in culture, religion, society between countries that are in East Asia and country that is in North Africa than between 2 central European countries.
So grouping countries by foreign born by continent is not so accurate, because it can be very misleading, especially in case of Asia-there are huge differences if you have people from Midle East or Indian subcontinent or East Asia and so on.
Obviously American cities are mostly diverse, but we can discuss what kind of diversity it is when you have 1/4 of population AfroAmerican - people that are all Americans by culture and everything, because they ancestors came 3 centuries ago and another 1/4 Hispanics, from that huge majority Mexican. Yes there are differences between Latin American countries, 1st is Carribean, another Andean, one has huge Amerindian population, another strong african and so on. But in the end in such city half of the city is Afro American and Mexican - with 1st being Americans for generatons just different by looks to Americans of Irish, German, Anglo, Polish and so on ancestries and 2nd group just speaking Spanish with some mestizo looks and Mexican culture and heritage - so if half of city is one of those 2 and rest is of Irish, German, Polish, British, Scandinavian, Italian descent with few Asians - is such city diverse by american standards? i don ´t think so and if you look at US diversity index many cities like this one i gave as example are counted as very diverse - i disagree.
Most diverse cities should have people from all around the world. How i said many US cities are diverse, but in the end not so much, because they have maybe 4-5 ,,groups,, while there are cities with 100 different ,,groups,,
NYC, London or Toronto are indeed most diverse cities in the world based on this criteria - having people from all corners of this planet representing high % of total population.
Especially NYC is best example of this. Shares of non-hispanic whites, Latinos, Black population and Asians is pretty even, no group dominating or even coming close to large minority.
Share of non-hispanic whites is decreasing every year since peak European immigration wave from late 19th, early 20th century. Today most of those people are what 4th, 5th, 6th generation? Huge majority of theam speaking only English, being Americanized, but having some identity and cultural aspects - remembering Italian, Polish, German, Jewish roots and so on.
Minority of white non-hispanics are relatively new immigrants and 2nd generation immigrants from former eastern bloc, good number of Russians and Jews from former Soviet countries
Black population of NYC - most are African Americans-what 10th-20th generation who knows exactly when they ancestors were forcefully brought to USA(back than actually not USA, but british colonies) from Western Africa, those people speak only English and are Americanized. Remaining minority/growing in share/ are immigrants and their descendats from black Carribean and Subsaharan Africa with their cultures, languages, differences./mostly Jamaica, Haiti, Guyana,Trinidad and Tobago(last 2 with large indian share) and Nigeria, Ghana, Kenya, Ethiopia, Somalia.
Hispanics - from every hispanic country there are people in NYC in good numbers. While most of US diverse cities is dominated by Mexicans/from 51% to 90% in some cases among Hispanics/ in NYC Puerto Ricans and Dominicans are largest groups with Mexicans on 3rd place. Than comes Ecuador, Colombia, El Salvador, Honduras and Peru. True diversity among Hispanics - not like in some other cities were Mexicans are huge majority, while they all speak Spanish there are many differences between Mexicans, Carribean Latinos and South Americans.
Asians - this is the most diverse group itself, because Asia is huge and there are tremendous differences in culture, religion and everything between certain countries, even regions inside Asia. In US census is Western Asia, Caucasus and part of Central Asia not counted to Asians. Anyway huge communties of Chinese, Indians, Bengalis/Bangladesh/, Pakistanis, Filipinos, Koreans with practically every ethnicity represented.
Than rest of NYC are people from Midle East, Asia Minor, Caucaus, North Africa, Central Asia and very few peple from North Asia/various ethnicities from Asian part of Russian Federation. Also i forgot on Native Americans and Pacific Islanders and peple from Australia and Oceania - obviously many from there are mixed or Australians of English, Italian ancestry and so on.
NYC is clearly city that is truly diverse with everyone living in there, mostly thanks to the fact that NYC is known melting pot and city based on immigration - also most popular/famous city in USA - thanks to TV, movies and so on worldwide glamour of NYC means it is magnet for immigrants to this days. Arguably most famous and recognized city in the world
NYC Population
This is good publication concerning foreign born population of NYC - latest edition
Toronto is currently above half belonging to visible minorities - mostly South Asians, Chinese, Blacks/predominantly Caribbean, Filipinos, West Asians/Arabs,Persians and it is truly city full of everyone with ethnic neighbourhoods.
London - in census from 2011 - over 44% was white British, today it is probably between 35-40% including people that are 4th generation Irish or Polish, rest is from Europe, South Asia, Caribbean, Africa, Eastern and Southeastern Asia.
London as capital of largest empire ever had people from their colonies long time ago, but large scale immigration happened only after WW2 with recruiting of Black Caribbeans and after partition of India in 1947. Today London has also people from all around the world and it has similar status to NYC - global alpha city one of most visited most famous and so on.
Now there are other cities that are very diverse - Paris, Amsterda or Brussels in Europe are probably most diverse after London - if we speak about capitals and 1 city per country. Than there are cities in german speaking Europe like Frankfurt, Vienna, Zurich that are half of migration background-that means 1st and 2nd generation, but mostly Europeans.
In USA i can´t really decide which city is No.2. Los Angeles is pretty diverse but in the end half of the city or county is Hispanic/predominantly Mexican or like 90% from Hispanics Mexican and Central American, so basically only other half has diversity outside of Latin America - with statistically largest Persian and Armenian communities among major US cities.
Miami even less diverse than L.A. - majority is Hispanic 2/3 actually - from that half Cuban and other half similar shares of South Americans, Central Americans and rest of Caribbean.
From remaining 1/3 of population mostly non-hispanic whites and blacks/good balance between Caribbeans, Afro Americans and some Subsaharan Africans.
Sydney, Melbourne and Auckland are also very diverse - to large Asian share, but very diverse too with whole world there. I would place them in top 10, top 15 for sure.
Vancouver is in most rankings in top 5 as one of the most diverse cities which i disagree, basically people there are of european origing or Asians/predominantly Chinese, South Asians and rest SE Asia. Very small share of total population is from rest of the world so not so diverse after all.
Based on many estimations, NYC, London and Toronto are top 3 in diversity with representing whole world, pretty evenly.
Btw some Latin American cities are also pretty diverse thanks to European colonization- that means native population that was there, later Africans brought there, European mass immigration and in some cases also Asians, for example century ago Sao Paolo or Buenos Aires were as much immigration cities like NYC - in all cases Europeans were huge majority of newcomers.
Also many cities in Africa are diverse, having people from tens if not hundreds ethnicities there speaking different languages with cultural differences, but it is mostly about African diversity-which is super diverse continent, but obviously those major african cities lack any immigration from rest of the world.
Similar case some major Indian cities with many ethnicities, languages and cultures but in the end eveyone there is from India.
Singapore or Kuala Lumpur are probably most diverse cities in Asia, but it´s mostly about varous Asian people there and some Europeans, Americans, Canadians, Australians not whole world really.
Midle East is specific region right now - Dubai, Abu Dhabi, top Saudi cities and some other capitals in region have huge foreign born population - Dubai is right now like 80% foreign - huge majority from that immigrants from Southern and SE Asia with other Arabs and some westerners for job reasons. But it is different in that case that most will go back, will never get citizenship, never be ,,locals,, and are treated like slaves in some cases/many cases/ - very specific and not so diverse with strong muslim authorities there.